I think they are imitations.
• The surface has some small blemishes and other characteristics that look like imitations I've seen.
• I see what looks like excess coating near some drill holes.
• The size, color and luster are too uniform.
• The smaller pearls next to the clasp is something I've seen with many imitations.
• The way the pearls connect with the clasp is low end. (Lack of French wire to protect the thread; split rings.)
Do these simple tests:
1. Rub 2 of the pearls together gently. Imitation pearls will glide smoothly; real nacre feels a bit gritty.
2. Real pearls are cooler than imitation pearls. If you have any pearls that you know to be real (or that you know to be fake), put these and the other pearls in the same temperature environment for about 30 minutes, and then hold them against your lip (which is very sensitive to temperature) and compare.